Drill bit

ABSTRACT

A drill bit constructed to improve a tip end of the cutting pointed portion to efficiently discharge chips from a center portion of a crush face of a drill hole to thereby improve cutting efficiency, is disclosed. A plurality of cutting blades  3   a   , 3   b , and  3   c  are formed to be arranged in a circumferential direction of a cutting blade chip  3  formed by a cemented carbide block body. The cutting blades  3   a   , 3   b , and  3   c  are each structured to have a cutting edge  4  formed by an edge between a face  6  and a flank  7  of the associated cutting blades. In this drill bit, a groove  8  is configured to be provided in a center portion of the tip end of the cutting blade chip in contact with tip ends of the cutting blade chip, and the tip ends of the cutting edges  4  have pointed portions.

The present application claims the benefit of priority of InternationalPatent Application No. PCT/JP03/13981 filed on Oct. 31, 2003, whichapplication claims priority of Japanese Patent Application No.2002-319611 filed Nov. 1, 2002. The entire text of the priorityapplication is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a drill bit constructed such that acutting blade chip made of cemented carbide is fixedly attached to a bitbody by brazing, welding, or the like. More particularly, the presentinvention relates to a drill bit which is suitable for use in drillingholes in concrete, stone, etc.

BACKGROUND ART

Drilling holes in concrete, stone, etc, is done by attaching a dedicateddrill bit to a rotating hammer drill and by applying both an axialvibrational striking force and a rotational torque to the drill bit. Inorder to meet demands for high efficiency in a drilling operation, adrill bit is typically constructed such that a cutting blade chip madeof cemented carbide which has high wear resistance is fixedly attachedto a tip end of the cutting edge of a bit body of the drill bit bybrazing, welding, etc.

The applicant has already proposed a drill bit of this type which isused exclusively for drilling holes in concrete, stone, etc, and isconstructed such that a cutting blade chip fixedly attached to a lowerend portion of a bit body has a plurality of cutting blades, eachcutting edge is formed by an edge between a face and a flank of thecutting blades, tip ends of the cutting edges of the cutting blades arecoupled at a center thereof to form a pointed shape without a chiseledge, a concave portion formed between the cutting blades is continuouswith a chip discharge groove formed on an outer periphery of the bitbody (for example, see Japanese Laid-Open Patent Application PublicationNo. 2002-178328).

Assume that the above mentioned drill bit without the chisel edge isattached to a rotating hammer drill and carries out drilling holes in aconcrete, stone, etc. In a cutting operation (striking and cuttingoperation) carried out by applying an axial vibrational striking forceto a crush face of a drill hole, i.e., by striking a tip end of thecutting edge to the crush face of the drill hole, the crush face of thedrill hole may be crushed, and then a bit rotates to cut the crush faceof the drill bit which has become fragile due to prior striking andcutting. In this manner, the drilling operation progresses.

In this case, the degree to which the crush face of the drill hole iscrushed by striking becomes larger at a center portion of the tip end ofthe cutting edge of the pointed shape into which tip ends of the cuttingedges are adapted to gather.

However, when the cutting operation is carried out by rotation of thebit, a cutting ability is low at the center portion of the tip end ofthe cutting edge because rotation track is not substantially drawn. Inaddition, since chips are inefficiently discharged from a center portionof the crush face of the drill hole which is conically recessed, theytend to remain there. The center portion of the cutting edges repeatedlystrikes the remaining chips. This reduces cutting efficiency of strikingand cutting.

Accordingly, an object of the present invention is to provide a drillbit capable of improving a tip end portion of cutting edges to reducechips remaining in a center portion of a crush face of a drill hole tothereby improve cutting efficiency.

In order to solve the above described problem, there is provided a drillbit comprising a cutting blade chip formed by a cemented carbide blockbody, the cutting blade chip having a plurality of cutting bladesarranged in a circumferential direction of the cutting blade chip toextend radially outward, the cutting blades being each structured tohave a cutting edge formed by an edge between a face and a flank of thecutting blades, the cutting edges extending radially outward such thattip ends are positioned on a tip end portion of the cutting blade chip,wherein a groove is configured to be provided in a center portion of thecutting blade chip in contact with tip ends of the cutting edges, andthe tip ends of the cutting edges have pointed portions.

In accordance with the drill bit constructed as described above, the tipends of the cutting edges are formed in contact with the groove and havea pointed shape. Therefore, when the drill bit is attached to therotating hammer drill and used for drilling holes in concrete, stone,etc, it strikes the crush face of the drill hole. In this case, thepointed portions at the tip ends of the cutting edges which are close toeach other strike the crush face of the drill hole at the same time. Forthis reason, the crush face of the drill hole is also crushed to aregion corresponding to the pointed portions (groove portions), andchips being generated at the crush face of the drill hole are left inthe groove. In this state, when the drill bit continues to rotate, thepointed portions of the tip ends of the cutting edges draw a rotationtrack. In the rotation and cutting operation performed by the cuttingedges, the entire cutting edges (over an overall length) entirely cutthe crush face of the drill hole which has become fragile due to priorstriking and cutting. In addition, the chips left in the groove afterprior striking and cutting operation is discharged outside the groovewithout substantial resistance by the rotation of the groove. Since thechips remaining in the center portion of the crush face of the drillhole is reduced, cutting efficiency improves.

The groove may be formed to cross an axis (axis extending in alongitudinal direction of the drill bit) of the drill bit at asubstantially right angle, the groove may be structured to have a faceof a circular-arc shape as viewed from a side such that a width of thegroove increases from a deepest point thereof toward the tip end of thecutting edge. In this structure, a circular-arc face of the groove isinclined toward the tip end of the cutting edge, and the pointed portionof the tip end of the cutting edge is formed substantially by an apex ofthree inclined faces including the face and the flank of the cuttingblade, and the circular-arc face of the groove. This increasesresistance to impact. Therefore, deformation or wear of the pointedportions of the tip ends of the cutting edges are reduced, regardless ofrepeated striking and cutting operation with respect to the crush faceof the drill hole. As a result, cutting performance is stable. Further,since the groove has the circular-arc face, the chips easily move in thegroove and are easily discharged from the groove.

While the number of the cutting blades is not specifically limited inthe drill bit of the present invention, the cutting blades may be formedby three cutting blades arranged at uniform (equal) intervals in acircumferential direction thereof, the three cutting blades may bestructured such that the tip end of the cutting edge of one of the threecutting blades is positioned at one end portion of the groove, and thetip ends of the cutting edges of remaining cutting blades are positionedat intermediate portions of the groove, and an opposite end portion ofthe groove is positioned in a concave (trough) portion formed between aface and a flank of associated cutting blades. In this structure, theconcave portion in which the end portion of the groove is positionedleads to the chip discharge groove formed on the outer periphery of thebit body through the concave portion formed between the cutting blades.Therefore, the chips are efficiently discharged from the groove.

The drill bit provided with the groove on the tip end side of thecutting edge is manufactured in a simple process in such a manner thatthe tip ends of the cutting edges are coupled to each other at the tipportion of the cutting blade chip to form the pointed portions and thenthe groove is formed on the tip end side of the cutting edge. As aresult, a drill bit (product) which has cutting edges and pointedportions with a high finish precision and has high quality is easilymanufactured with high productivity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of components of a drill bit according to anembodiment of the present invention, a part of which is omitted;

FIG. 2 is a bottom view of the drill bit of FIG. 1;

FIG. 3 is a bottom view of a drill bit according to another embodimentof the present invention, showing a structure in which cutting bladesare arranged at non-uniform intervals in a circumferential direction ofthe drill bit;

FIG. 4 is a bottom view showing a construction of a drill bit accordingto another embodiment of the present invention, having two cuttingblades;

FIG. 5 is a bottom view showing a construction of a drill bit accordingto another embodiment of the present invention, in which a groove isdumbbell-shaped;

FIG. 6 is a bottom view showing a construction of a drill bit accordingto another embodiment of the present invention, in which the groove istrefoil-shaped;

FIG. 7 is a side view of components of a drill bit according to anotherembodiment of the present invention, in which a bottom face of thegroove is inclined in one direction; and

FIG. 8 is a side view of components of a drill bit according to anotherembodiment of the present invention, in which the bottom face of thegroove is inclined in opposite directions to form a pointed shape.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of a drill bit according to the presentinvention will be described with reference to the drawings.

(Embodiment 1)

Turning now to FIGS. 1 and 2, a steel bit body 1 is shown. A shank (notshown) extends upward from the bit body 1 and is coupled to a driveshaft of a rotation hammer drill. Chip discharge grooves 2 are formed onan outer periphery of the bit body 1. A cutting blade chip 3 formed by acemented carbide block is fixedly attached to a tip end of the bit body1 by brazing, welding, or the like. The cutting blade chip 3 has cuttingblades 3 a, 3 b, and 3 c arranged in a circumferential directionthereof. Concave portions 5 are each formed between the cutting blades 3a and 3 b, 3 b and 3 c, and 3 c and 3 a and lead to the chip dischargegrooves 2 of the bit body 1. Each cutting blade 3 a, 3 b, or 3 c has acutting edge 4 formed by an edge between a face 6 and a flank 7 of theassociated cutting blades.

In the present invention, when the cutting edge 4 is formed in eachcutting blade 3 a, 3 b, or 3 c, tip ends of the cutting edges 4 arefirst caused to gather to form a pointed shape without chisel edge at atip end of the cutting edge. Then, after the cutting edges 4 are formed,a groove 8 is formed at the center portion of the tip end of the cuttingedge to extend in a direction substantially perpendicular to an axialdirection of the bit body 1 to form a pointed portion 9 at the tip endof each cutting edge 4.

In this embodiment, a groove face of the groove 8 is formed in acircular-arc shape As shown in FIG. 1, the groove 8 is formed to have agroove face having a width that increases from a deepest point towardthe tip end of the cutting edge.

Specifically, as shown in FIG. 2, the pointed portion 9 of the tip endof the cutting edge 4 of the cutting blade 3 b is positioned at one endportion of the groove 8, and the pointed portions 9 of the tip ends ofthe cutting edges 4 of the remaining cutting blades 3 a and 3 c areformed at intermediate portions of the groove 8. An opposite end portion8 a of the groove 8 is positioned in a concave (trough) portion 5 aformed by the face 6 and the flank 7 between the cutting blades 3 a and3 c. The concave portion 5 a lead to the chip discharge groove 2 formedon the outer periphery of the bit body 1 through the concave portion 5between the cutting blades 3 a and 3 c.

A basic construction of the drill bit having another construction issimilar to that of the drill bit which is well known. Therefore, thewell-known drill bit is replaced by this drill chip for use in drillingholes.

In accordance with the drill bit of the present invention, when eachcutting edge 4 strikes the crush face of the drill hole to cause thecrush face of the drill hole to be subjected to a striking and cuttingaction, it strikes and crushes the crush face of the drill hole. In thiscase, since the pointed portions 9 of the tip ends of the cutting edges4 are close to each other and strike the crush face of the drill hole,the crush face of the drill hole is crushed in the vicinity of thepointed portions 9 to a region of the center portion of the tip end ofthe cutting edge corresponding to the groove 8. A part of the chipsbeing generated at this time are left in the groove 8. In this state,when the drill bit continues to rotate, the pointed portions 9 of thetip ends of the cutting edges 4 draw a rotation track. Therefore, thecutting edges 4, including the pointed portions 9, entirely rotate andstrike the crush face of the drill hole which has become fragile due toprior striking and cutting action. At this time, since the groove 8rotates, most of the chips remaining in the groove 8 is discharged fromthe groove 8 into the chip discharge groove 2 through the concaveportion 5 a without substantial resistance by the rotation of the groove8. As a result, the chips remaining in the crush face of the drill holedecreases, thus carrying out a smooth drilling operation.

While the drill bit having the cutting blades 3 a, 3 b, and 3 c arrangedat uniform (equal) intervals has been described in the above embodiment,they may alternatively be arranged at non-uniform intervals as shown inFIG. 3. In further alternatives, as shown in FIG. 4, the cutting blades3 a and 3 b may be arranged at two locations and at uniform ornon-uniform intervals, or otherwise may be arranged at four or morelocations and at uniform or non-uniform intervals, although not shown.

The groove 8 may be configured in an elongated circle shape havingsemicircular portions at both ends as viewed from the bottom as shown inFIG. 2, or may be configured in a dumbbell-shape as viewed from thebottom as shown in FIG. 5. Or, as shown in FIG. 6, the groove 8 may beconfigured in a trefoil shape, or in other shapes. A bottom 8 c of thegroove 8 may be formed to extend in the direction perpendicular to theaxial direction of the bit, or may be inclined as indicated by a brokenline of FIG. 7. Or, as indicated by a broken line of FIG. 8, the bottom8 c of the groove 8 may be configured to be inclined in oppositedirections to form a pointed portion. Further, as viewed from thebottom, the longitudinal direction of the groove 8 may conform to thelongitudinal direction of the cutting edges 4, or they may form acrossing angle between them. In FIGS. 3 through 8, the same referencedesignators as those in FIGS. 1 and 2 denote the same or correspondingparts.

In accordance with the drill bit of the present invention, since the tipends of the plurality of cutting edges are in contact with the grooveformed at the tip portion of the tip end of the cutting edge and formspointed portions, the crush face of the drill hole is crushed to theregion corresponding to the groove in the striking and cutting operationwhich is adapted to cause the cutting edges to strike the crush face ofthe drill hole. As a result, a crushing action which is superior to thatof the conventional drill bit is provided. In addition, in the cuttingoperation by rotation which is adapted to cause the cutting edges tostrike and cut the crush face of the drill hole, the tip ends of thecutting edges also draw a rotation track. Thus, the cutting operation iseffectively performed. Further, since the groove enables the chips to beefficiently discharged from the center portion of the crush face of thedrill hole, the chips remaining in the crush face of the drill holedecreases. Therefore, cutting efficiency is improved. Moreover, thedrill bit is manufactured in a simple process for forming the groove atthe tip portion of the cutting edges. As a result, a drill bit (product)which has a tip end of the cutting edge with a high finish precision andhas high quality is easily manufactured with high productivity.

INDUSTRIAL APPLICABILITY

The drill bit of the present invention is used as a drill bit suitablefor use in drilling holes in concrete, stones, etc.

1. A drill bit comprising: a cutting blade chip formed by a cementedcarbide block body, the cutting blade chip having a plurality of cuttingblades arranged in a circumferential direction of the cutting blade chipto extend radially outward, the cutting blades being each structured tohave a cutting edge formed by an edge between a face and a flank of thecutting blades, the cutting edges extending radially outward such thattip ends are positioned on a tip end portion of the cutting blade chip,wherein a groove is configured to be provided in a center portion of thecutting blade chip in contact with tip ends of the cutting edges suchthat the groove has an elongated circle shape formed by semicircularportions as viewed in a bottom view and has a bottom, and the tip endsof the cutting edges having pointed portions.
 2. The drill bit accordingto claim 1, wherein the groove is formed to cross an axis of the drillbit at a substantially right angle, and the groove is structured to havea face of a circular-arc shape as viewed from a side such that a widthof the groove increases from a deepest point thereof toward the cuttingedge tip end.
 3. The drill bit according to claim 1, wherein the cuttingblades are formed by thee cutting blades arranged at uniform intervalsin a circumferential direction thereof, the three cutting blades arestructured such that the pointed portion of the top end of the cuttingedge of one of the three cutting blades is positioned at one end portionof the groove, and the pointed portions of the tip ends of the cuttingedges of remaining cutting blades are positioned at intermediateportions of the goove, and an opposite end portion of the groove ispositioned in a concave portion formed between a face and a flank ofassociated cutting blades.
 4. The drill bit according to claim 2,wherein the cutting blades are formed by thee cutting blades arranged atuniform intervals in a circumferential direction thereof, the threecutting blades are structured such that the pointed portion of the topend of the cutting edge of one of the three cutting blades is positionedat one end portion of the groove, and the pointed portions of the tipends of the cutting edges of remaining cutting blades are positioned atintermediate portions of the goove, and an opposite end portion of thegroove is positioned in a concave portion formed between a face and aflank of associated cutting blades.
 5. A drill bit comprising a cuttingblade chip formed by a cemented carbide block body, the cutting bladechip having a plurality of cutting blades arranged in a circumferentialdirection of the cutting blade chip to extend radially outward, thecutting blades being each structured to have a cutting edge formed by anedge between a face and a flank of the cutting blades, the cutting edgesextending radially outward such that tip ends are positioned on a tipend portion of the cutting blade chip, wherein a groove is configured tobe provided in a center portion of the cutting blade chip in contactwith tip ends of the cutting edges such that the groove has a dumbbellshape as viewed in a bottom view and has a bottom, and the tip ends ofthe cutting edges have pointed portions.
 6. The drill bit according toclaim 5, wherein the groove is formed to cross an axis of the drill bitat a substantially right angle, and the groove is structured to have aface of a circular-arc shape as viewed from a side such that a width ofthe groove increases from a deepest point thereof toward the cuttingedge tip end.
 7. The drill bit according to claim 5, wherein the cuttingblades are formed by thee cutting blades arranged at uniform intervalsin a circumferential direction thereof, the three cutting blades arestructured such that the pointed portion of the top end of the cuttingedge of one of the three cutting blades is positioned at one end portionof the groove, and the pointed portions of the tip ends of the cuttingedges of remaining cutting blades are positioned at intermediateportions of the goove, and an opposite end portion of the groove ispositioned in a concave portion formed between a face and a flank ofassociated cutting blades.
 8. A drill bit comprising a cutting bladechip formed by a cemented carbide block body, the cutting blade chiphaving a plurality of cutting blades arranged in a circumferentialdirection of the cutting blade chip to extend radially outward, thecutting blades being each structured to have a cutting edge formed by anedge between a face and a flank of the cutting blades, the cutting edgesextending radially outward such that tip ends are positioned on a tipend portion of the cutting blade chip, wherein a groove is configured tobe provided in a center portion of the cutting blade chip in contactwith tip ends of the cutting edges such that the groove has a trefoilshape as viewed in a bottom view and has a bottom, and the tip ends ofthe cutting edges have pointed portions.
 9. The drill bit according toclaim 8, wherein the groove is formed to cross an axis of the drill bitat a substantially right angle, and the groove is structured to have aface of a circular-arc shape as viewed from a side such that a width ofthe groove increases from a deepest point thereof toward the cuttingedge tip end.
 10. The drill bit according to claim 8, wherein thecutting blades are formed by thee cutting blades arranged at uniformintervals in a circumferential direction thereof, the three cuttingblades are structured such that the pointed portion of the top end ofthe cutting edge of one of the three cutting blades is positioned at oneend portion of the groove, and the pointed portions of the tip ends ofthe cutting edges of remaining cutting blades are positioned atintermediate portions of the goove, and an opposite end portion of thegroove is positioned in a concave portion formed between a face and aflank of associated cutting blades.